Abstract

Random lasing in nanocrystalline Nd3+:YVO4 powder is demonstrated. A method that analyzes the decay kinetics after long-pulse excitation is used to determine the laser characteristics. This method permits to measure the fractional contribution of spontaneous and stimulated emission as well as upconversion as a function of the pump intensity. We observed that maximum linewidth narrowing is achieved when the stimulated emission reaches 50% of fractional contribution in the backscattering cone.

(a) Disk-like sample confined by microscope slides. The line at the center of the disk (arrow) is due to visible emission from the upconversion process. (b) SEM image from the extremity of the sample. (c) SEM image from the center of the sample.

Experimental setup: The 809 nm diode beam is first shaped by two cylindrical lenses with focal lengths of −13 mm and −25 mm, respectively, and then focused on the sample with a spherical f = 20mm lens. The backscattering cone (BC) was separated from the pump excitation by a beam splitter (BS) and captured by fiber coupled detectors.

(a) Beam waist measured in horizontal and vertical direction at the sample position as a function of distance from the focusing lens. (b) Beam profile observed with focusing lens at 26 mm and (c) at 35 mm.

Linewidth narrowing and fraction of stimulated emission at 1064 nm versus the pump power. The double arrows show that at a pump intensity of 15 W/mm2 maximum linewidth narrowing is achieved and at the same time 50% of stimulated emission is detected.

(a) Determination of the radiative lifetime of the 4F3/2→4I11/2transition for a Nd:YVO4 bulk with 3 mm thickness. Fitting curve made with a third order polynomial. (b) Integrated lifetime at the center of the compressed pellet.

(a) 4F3/2→4I11/2 spontaneous transition decay and fit with Eq. (3) for a pump intensity of 8.3W/mm2 (b) spectra of up-conversion emissions. (c) Saturation of the up-conversion rate as a function of the pump intensity.